Once you fill it with eggs,watch the temps plumment for hours.Holes open or closed will depend on how much water is inside the bator,,and air circulation or not.With a still air,misting is effective as well as more surface area for the water to evaporate from,,where if a fan is used,less surface area is needed because of the air being forced over the sponges,or holding area.As eggs hatches the humidity levels rise a lot,,then they will drop off as the chicks dries off hours later.I would assume that once your eggs are all placed in the bator,,and reach 99.5 degrees,you will be worried if your preset temp now will get high enough.You may have to "tweek" a little at a time again,until all eggs are at the right temp.